1. Field of the Invention
The present invention relates to a crystalline iron phosphate doped with metals, a method of preparing the same, and an olivine-structured lithium composite metal phosphate prepared therefrom, and more particularly to a crystalline iron phosphate doped with a metal (MFePO4, hereinafter referred to as an MFP), which is used as a precursor of an olivine-structured lithium composite metal phosphate (LiMFePO4, referred to as an LMFP) used as a cathode active material for lithium secondary batteries, and a method of preparing the same.
2. Discussion of Related Art
In general, as an olivine-structured LMFP used as a cathode active material for lithium secondary batteries, an LMFP (LiMFePO4) doped with a different type of metals has been prepared by mixing different types of metals in a solid state.
However, when a raw material in a solid state is present in a method of preparing an LMFP, in order to prepare nano-sized LMFP particles, there are problems in that particulate raw materials should be used; the raw materials should be pulverized; there are many restrictions on the controls of the shape and size of the particles as compared with a liquid state method; and in case of adding two types or three types of metals at a position of M, there is a potential that a solid solution such as LiFe1-xMxPO4 is not properly formed but is present in a state of being separated into LiFePO4 and LiMPO4.
Therefore, the present inventors found that when a crystalline iron phosphate used as a precursor of an LMFP is prepared, that is, in a case in which while a small quantity of a different type of metals is added during crystallizing an amorphous iron phosphate to prepare a crystalline iron phosphate, a metal doping is induced, efficiency on preparing an LMFP from a crystalline iron phosphate doped with metals can be increased and the processing costs can be reduced. Therefore, the present inventors completed the present invention.